Integrated circuits are used in a wide variety of applications. Systems ranging from personal computers to automobiles rely on integrated circuits to function properly. In these systems, the integrated circuits process data based on electronic signals input to the integrated circuit. The integrated circuits produce output signals for the system in response to the input signals. Further, the integrated circuits often use internal electronic signals in producing acceptable output signals. Depending on the type of integrated circuit, it typically includes circuits that regulate the internal electronic signals to stay within an acceptable range so that the integrated circuit operates properly.
An example of a data storage or memory device having such internal voltage regulation circuits is a dynamic random access memory (DRAM). Conventional DRAMs include memory arrays with intersecting row and column lines coupled to individual storage cells. Conventional DRAMs include an externally generated power supply (Vcc) and a common ground. The devices of the DRAM use the common ground and power supply voltages in order to function properly. Typical DRAMs also include a voltage (Vccp) that is above the power supply that drives the word lines of the DRAM. Also, the semiconductor substrate of the DRAM is usually biased below common ground with a back bias voltage (Vbb). A biased substrate gives better control over threshold voltages, reduces transistor leakage, and guards against latch-up.
Many DRAM circuits include voltage regulators that monitor voltages such as the pumped supply voltage or back bias voltage. Conventional voltage regulators attempt to maintain a substantially constant difference between the monitored voltage and a reference voltage, for example between Vccp and Vcc or between Vbb and common ground. The voltage regulators typically activate stabilizing circuitry when fluctuations occur in the monitored voltage. Conventional voltage regulators include an input stage designed with a trip point carefully adjusted to toggle at a desired voltage level. When the monitored voltage crosses the trip point of the input stage, a signal is generated and amplified to activate stabilizing circuitry to correct the variation in the monitored voltage. While this type of voltage regulator is useful, it is typically difficult to implement. The actual value of the monitored voltage is a function of diode voltage/current, input stage trip point, and cumulative amplifier gain. Possible variations in these interactive factors complicate the realization of this type of voltage regulator. Additionally, high crossing currents are generated when this type of voltage regulator is operated near the input stage trip point.
Designers have tried to overcome these difficulties by implementing voltage regulators that include a voltage translation stage and a differential comparator stage. Although these differential voltage regulators are more readily implemented, their operation is unpredictable due to fluctuations in externally generated power signals. The voltage translation stage of conventional differential voltage regulators are sensitive to fluctuations in Vcc, causing non-linearities and incorrect operation. Further, these differential voltage regulators may not operate correctly due to non-linearities of the differential amplifier in the differential comparator stage.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a voltage regulator that more accurately and consistently regulates an input voltage.